(1) Field of the Invention
The present invention relates generally to lifting devices and more specifically in one possible embodiment to a dampened one-axis pivoting lifting device for a multi-line lift configuration.
(2) Background of the Invention
In the maritime field, a lifting device is often used to grab or capture water vehicle such as unmanned underwater vehicles. The lifting device is typically a rigid frame that is clamped to the vehicle. The rigid frame provides lifting points to which multiple lift cables can be attached. Once the frame is secured to the underwater vehicle, a ship-borne crane lifts the water vehicle from the water.
However, the lifting process often takes place in a dynamic fluid environment that may comprise wind and waves that may cause the ship-borne crane and/or water vehicle to move relative to each other. In this environment, the water vehicle, which may be relatively heavy, is likely to experience rolling movement along the axis of the vehicle.
As the vehicle being lifted rolls in the water environment, some lines slacken while at some point during the roll, one or more other lines suddenly become taut. When these lift lines suddenly become taut, they must resist the entire weight and momentum of the vehicle that suddenly comes to bear. These dynamics can snap the lift lines during the recovery operation and/or cause damage to the vehicle as the frame engages the vehicle at stress points. Accordingly, this type of suddenly applied stress may be referred to herein as a “snap load”.
If a lift line breaks or if there is damage to the frame or vehicle due to a snap load, the lifting operation can be significantly prolonged. Equipment damage may occur to both the vehicle and lifting device. Moreover, breaking lines and/or equipment can potentially lead to unsafe environment for workers assisting in the capture of the underwater vehicle.
Consequently, those of skill in the art will appreciate the present invention, which addresses the above and/or other problems.